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  #1  
Old 11-24-2020, 04:02 PM
Keldog Keldog is offline
 
Join Date: Nov 2016
Location: Grass Valley, CA
Posts: 35
Default Need advice

Strange thing happened twice now when shutting down from a flight. Idle in towards hangar after taxiing at about 2000 rpm's for 2 minutes, idle back to 1800 rpm's before shutdown, then off avionics, off Ignition A, off Ignition B, off master. Instead of immediately coming to a halt as normal, the engine continued to stumble on very roughly. Not sure what to do, I pulled the choke out and it finally rotated to a stop. First time it did it about 3 weeks ago, I thought maybe bad ground on one of the ignitions. So I took off the top cowl, checked all the connections on both modules and followed ground wires to eventual source to confirm all is tight. All good. Taxi to run up to check for normal rpm drop/delta of both ignitions; all good. Flew since first instance 4 times now with no more issues on shut down. Sunday flew to KTVL for breakfast with the better half and again....stumble on shut down; had to engage choke to get it shut down. After breakfast, started up fine, flew back home, same issue on shut down at home hangar.

Instinctively; I think I know what you guys are going to tell me to do; but thought it best to describe in detail what I experienced first.

Advice and direction is greatly appreciated!
2011 RV12 # 120201 395 hours
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  #2  
Old 11-24-2020, 04:44 PM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,204
Default

Sounds like one of the CD ignitions is not shutting off. Could be bad panel switch or intermittent connection to main panel.

Try shutting off one ignition at a time in cruise flight. You should notice a reduction in RPM when each ignition is shut off.

Try shutting down engine ignitions instead of A then B - try B then A.

Try shutting Master Switch off then shut ignitions per above...
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Jim Stricker
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 633

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H
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  #3  
Old 11-24-2020, 04:59 PM
DHeal DHeal is offline
 
Join Date: Sep 2006
Location: Windsor, California
Posts: 944
Default

My RV-12 experienced an intermittent internal failure of one of the panel-mounted ignition switches. It is a relatively easy fix with a new switch being available from Van's.
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EAA #23982 (circa 1965) - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B 2020) - N124DH flying since March 2014 - 990+ hours (as of Jan 2021)!
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  #4  
Old 11-24-2020, 09:21 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,889
Default

From your description it might be “dieseling”. Does it run hot?
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  #5  
Old 11-24-2020, 11:22 PM
NinerBikes NinerBikes is offline
 
Join Date: Dec 2018
Location: Granada Hills
Posts: 997
Default

I believe your idle speed should be set to 1650 rpm or less.

I turn off one ignition system at a time, with throttle set at the idle stop.

This makes the shut down of rotation of the prop much less violent when the rotation stops through the gear box.
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  #6  
Old 11-25-2020, 12:21 AM
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PaulvS PaulvS is offline
 
Join Date: Aug 2019
Location: Western Australia
Posts: 482
Default

Quote:
Originally Posted by NinerBikes View Post
I believe your idle speed should be set to 1650 rpm or less.

.
What spec are you using as a reference for the 912ULS? If idle speed is too low it is hard on the gearbox and causes wear.
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  #7  
Old 11-25-2020, 07:16 AM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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Quote:
Originally Posted by PaulvS View Post
What spec are you using as a reference for the 912ULS? If idle speed is too low it is hard on the gearbox and causes wear.
You are correct, uneven firing pulses at low speed is bad for the gearbox. Yes, set idle for ~ 1600 so engine can be slowed sufficiently in the air for good aerodynamic braking when prop is being back-driven in a glide. When engine is being back-driven the gear mesh is loaded heavily in one direction and gears run smooth. As airplane touches down the pilot must advance throttle to operate in green arc on the ground. Gears and rotating elements (bearings) can take a lot of abuse if rotating at high speed. Envision wheel bearings on a car hitting a huge pot hole. As long as wheel in rotating, rollers/ bearing race are OK. Now hit a bearing with hammer during installation and you have added small flats on the rollers and bearing will fail.

I start and warm my engine at ~ 2700 RPM so that initial uneven running of cold engine appears smooth for the gearbox. My shutdown procedure is idle slightly above 2000 RPM when switching off ignitions. Engine has over 600TT and gearbox is like new. Relative “health” of gears and drive dogs on overload clutch can be “inspected” by feel and sound when burping the engine for oil level check. Turn the prop slowly and feel for backlash in the drive dogs when compression goes over TDC. Also rock the prop back/forth to feel gear mesh. Make a good mental picture for future comparison.
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Jim Stricker
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 633

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H
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  #8  
Old 11-25-2020, 07:41 AM
DBRuth DBRuth is offline
 
Join Date: Nov 2013
Location: Cumming,GA
Posts: 101
Default Operator's manual

You might want to read the operator's manual and see what it says about dieseling and proper shut down procedure. I have not looked at the procedure lately so I can't remember the instructions. The idle on my engine is set about 1600-1650, but I don't ever operate that low. Try not to let it get below 1950revs at any time. My shut down procedure is to reduce idle to 1950 momentarily, then back to min idle and quickly shut off one ignition, watch for rpm drop, and quickly shut down second ign. Engine temperature and fuel quality/octane can also cause run-on/dieseling.
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  #9  
Old 11-25-2020, 07:50 AM
JBPILOT JBPILOT is online now
 
Join Date: Nov 2007
Location: Jesup, Iowa
Posts: 1,668
Default My experience - -

I had the same thing 2 - 3 years ago. Finally found the small connector with the two 'kill' wires must of had a little corrosion. Put electric cleaner spray on connector halves. Then dielectric grease. Fixed it. Simple to try.
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  #10  
Old 11-25-2020, 03:47 PM
Keldog Keldog is offline
 
Join Date: Nov 2016
Location: Grass Valley, CA
Posts: 35
Default

Thanks for the responses guys. A few answers to questions raised and another question:
JBPILOT and DHEAL - I think you're both talking about the same thing.(?) Is access for the switches from the front instrument panel or from the top through the avionics bay?
DBRuth and RFScaller - plane doesn't run hot and what is dieseling? I run 91 octane mogas 90% of the time and 100LL cross country. Occasionally i suppose I could have up to a 50/50 mix of the two in the tank as well.
Piper J3 - I will try the 3 tests in your reply from yesterday.

And here I thought all responses would point me towards the dreaded floats!
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